Promo blocks is automated system, that allows to create sets of promo blocks (promo block group) that later you can associate with the page you like (or with home page by default).
If you later decide to change promo block design you no longer need to each each of the content blocks to make it happen.
Also promo blocks offer statistic, like:
- unique view count
- unique click count
Also you can specify transition effect and effect settings for each of a promo block groups separately.
Days, when promo block (or DIP - dynamic image panel) was just a clickable image are long gone with HTML5, where image is just a background and you have text/links/buttons over that image and they are clickable too.